Miniature spectrometers based on MEMS technology (MEMS … Micro-Electro-Mechanical-System), also referred to as micro-spectrometers, are offering a number of highly desirable qualities for NDT: small size, high robustness and low costs, while promising reasonable performance levels comparable with those of conventional process spectrometers. Due to their unique properties micro-spectrometers allow flexible implementation in various NDT configurations. For instance, several different measurement positions can be realized simultaneously, without the need for optical multiplexing or elaborate optical fibre networks.
Micro-spectrometers have just recently matured to a level at which they can be applied in an industrial environment. Hence, this contribution is focusing on the current state-of-the-art and the actual application and evaluation of MEMS-based micro-spectrometers in various NDT situations. Spectra obtained with different devices will be compared with standard process spectrometers and analysed using multivariate statistics. A number of practical case studies will be presented. Among them the monitoring of component quality of fibre-reinforced plastic composites by measuring the curing degree and the mixing quality in real-time during the manufacturing process. Another application addresses NDT of multi-layer polymer films with a focus on chemical composition. The ability of infrared spectroscopy and multivariate data analysis to measure latent variables was exploited in a case study focusing on materials used for thermal energy storages – a use case where the low costs of micro-spectrometer devices were of particular importance. The results obtained within the different case studies confirmed the basic suitability of micro-spectrometer technology for spectroscopic NDT. Moreover, for specific applications they are even representing the key technology for reasonable spectroscopic NDT, especially from an economical point of view.